At what point do you replace the 12v battery?

wstt, the ground choice is probably poor. Look in the owners manual for the engine ground or try the strut tower nut/bolt.

moto g(7) power ?

 

+1. I usually find that the positive jump terminal, enclosed in the fuse box, has the metal in decent surface condition, but even unpainted metal exposed under the hood can have an oxide layer that's a surprisingly good insulator. I usually go for the bolts around the edges of the inverter cover, and if I've got a big enough clamp, put it over top and bottom. And scrape it back and forth some.

 

The stud/nut combo holding down the EGR valve is good too, very close.

 

I connected to the exact places the owners manual said to. I also tried several other ground spots. Autozone and O’Reilly’s also tried all over and got nothing. I’m wondering if there is a fuze to the positive terminal under the hood or something that could be bad.

 

First guess: That picture in your owners manual is really for a different model.
Second guess: One of your main battery connections is loose or corroded and it takes a SIGNIFICANT current demand for anything to flow.
What happens if you try to do the measurement with the car in "ready" mode.....on and running ??

On mine, the "jump point" is also a power distribution point for the WHOLE engine bay.
I don't think it is possible for that point to be dead and still have the car function.

 

The 12V battery is supposed to be about minimum 12.5V after we fully charge and remove surface charge (1 minute headlights on). Below that, it's time to do around.

 

There is a main power fuse beneath the fuse box that if failed, isolates the charge point. See this explanation and diagram, which may differ slightly for your year and model, but tell the tale:

2011 Prius not charging 12V system | Page 2 | PriusChat